Why bother writing grimdark fantasy when you can just try promoting your struggling work instead? The setting and tone's going to be about as bleak and nihilistic either way.
Why bother writing eldritch horror when you can promote your work instead? You'll end up with crippling existentialism either way, torn between putting effort into something you know will barely make a dent and simply writing your work in peace knowing it'll be an eternity before you get true recognition.
Of course, being a low-concept writer just makes it all hurt even more. I really wish I had something actually cool to market off of, like werewolves riding rocket-powered motorcycles.